Chimneys: where, why and do we even need them???

[kypreos]

Hi,

Apologies if these sound like silly questions - I've read three books and trawled through this and other forums and still can't get my head around this. Having seen lots of traditional ovens in Cyprus that don't seem to have vents / chimneys at the front...

Is a vent or chimney really necessary?

I'm also confused about where a chimney / vent should sit - should it sit in front of the door?

[pete123]

I think it is just to keep any smoke out of your eyes. They normally go in front of the door unless you put a flap (flap isn't really the right word) in the chimney to keep the heat in.

A chimney might help with air circulation as well?

[Happy Baker]

Helps draw the fire when you're lighting ... you need fuel, spark and air to have a successful fire, so the chimney is important to keep the hot air rising.
Mine is actually behind the door ...

[turkey]

there is no such thing as a silly question, only silly answers.

the answer is you do not "need" one. As you have seen and lots of cob builds prove they are not essential. The oven is very basic and a fire in it will eventually get up to temp, it will however smoke a lot as the fire will struggle to achieve a clean burn due to lack of oxygen and lower heat.

if you have a low fire you fan it and it burns better, this is due to the extra oxygen being introduced.

wood breaks down in heat and the smoke is un burnt carbon particles, this is flamable if you have enough heat and oxygen,

a chimney works a little like a car turbo, as the fire goes it heats the chimney and hot use entered, thus air will rise causing a vacuum pulling more warm air in which will rise... This then means there is a good flow of air going into the fire meaning it can burn hotter, this coupled with the extra oxygen means the carbon in the gas being released from the wood will also ignite, this jeans less smoke, more heat and more heat released per log (cheaper to run).

back in traditional times I suppose this was not known, people did not live on top of each other so smoke was less if a concern and wood was a free resource.

so you don't need it but it helps get to full burn faster and more economically with less smoke in your eyes.

[kypreos]

Thanks guys, esp. Turkey - much appreciated.

I'm planning on using my oven for slow-cooking - roasts, etc. rather than quick-cook pizzas. So I see my door being closed quite a bit of the time...

Is it correct to say that if the flue / vent / chimney is behind the door, then some form of damper is needed to block the chimney when the door is closed? And that by contrast, if the flue / vent / chimney is in front of the door, no damper is needed as the door will do the all the blocking?


Thanks again!

[tonyb]

That's right but if its mostly retained heat cooking you will be doing you need a plug made from insulation material rather than a damper ie movable flap.

[cannyfradock]

My twopennethwoth

"Is it correct to say that if the flue / vent / chimney is behind the door, then some form of damper is needed to block the chimney when the door is closed? And that by contrast, if the flue / vent / chimney is in front of the door, no damper is needed as the door will do the all the blocking?" .......correct.

You have posted this in the Pompeii construction board. If you look at the Pompeii oven builds most people build an internal arch which forms part of the dome. The entrance arch is slightly larger than the internal arch creating the rebate to take the door. This gives the oven it's full potential of Pizza party's, bread "batch" baking, slow roasts or casseroles and even the following day you could bake a cake......as long as the oven has correct insulation.

but.....as has been mentioned.....it's not compulsory.....it just makes retained heat cooking a lot easier.

Terry